(1) Field of the Invention
The invention relates to processes for packaging integrated circuit dies, and more particularly, to a method of packaging integrated circuit dies with a grounded stiffener.
(2) Description of the Related Art
A cavity-up ball grid array (BGA) package structure, schematically shown in FIG. 1, was originally patented by R. D. Schueller in 1999 in U.S. Pat. Nos. 5,866,949 and 5,990,545. In these patents, a chip scale BGA for integrated circuit (IC) packaging has a non-polymer layer or support structure 10 positioned between a chip 12 and a substrate 14. The non-polymer support layer may be a material, such as copper foil, having sufficient rigidity to allow processing of the chip scale package in strip format. The non-polymer support layer is conductive and could be electrically coupled to the integrated circuit to form a power or ground plane. The non-polymer support layer can be made of copper foil with a thickness of 100 μm-250 μm, but is not limited to copper foil. The adhesive layer may be any adhesive suitable for securing the non-polymer pad 10 to the flexible tape substrate 14. The adhesive layers have a thickness of between about 25 μm and about 75 μm, more typically between about 25 μm and about 50 μm. The stiffener functions as a ground plane and heat spreader by wire bonding and solder ball attachment on the stiffener.
FIG. 2 shows a die-up enhanced BGA with grounded stiffener 10 having wire bonding 21 from an integrated circuit die 12 to the stiffener 10 and thermal balls 20 attached to the stiffener 10 through holes in a substrate 14. This type of package is taught in U.S. Pat. No. 6,586,834 B1, by M. W. Sze et al, International patent application no. WO 2004/097896 A2 by Shelia E. Chopin et al, U.S. patent application Ser. No. 2005/0173787 A1 by S. Z. Zhao et al, and U.S. Pat. No. 7,005,737 B2 by S. Z. Zhao et al.
FIG. 3 shows a heat slug 25 attached to a bottom side of the stiffener 10 to provide the grounded stiffener for thermal enhancement of the die-up BGA packages. This design is disclosed in U.S. Pat. Nos. 6,825,108 B2, 7,078,806 B2, and 7,038,312, all by Reza-ur R. Khan, et al, and U.S. Pat. Nos. 6,876,553 B2 and 6,887,741 B2 by S. Z. Zhao, et al.